Optical distance measuring equipment

ABSTRACT

Distance measuring equipment that utilizes a light beam that is intensity modulated by a carrier frequency which is frequency modulated by subcarrier frequencies to provide accurate fine, medium, and coarse distance measurements by detecting the phase shift of these carrier and subcarrier frequencies as a function of distance, and which system includes a cross coupling light transmission means for removing internal delay phase shift error, and that employs a light attenuating device to equalize the intensity of the cross coupling illumination with the return illumination received, and that employs a light transmitter having a substantially planar light source.

ilnite et al.

Madigan Apr. 17, 1973 I 54.] OPTICAL DISTANCE MEASURING 3,428,815 2/1969Thompson ....356/5 EQUIPMENT 2,929,922 3/1960 Schowlow et al.....330/4.3 3,652,161 3/1972 Ross ..356/5 [75] Inventors: Thomas S.Madlgan, San Dlego;

Richard F. Stone; David C. Dunn, OTHER PUBLICATIONS z i :g g L:T Chen etal., Applied Optics, v61. 2, NO. 3, 3-1963,

I 0 350-97. 6 71. San Diego, all Of Calif. Tpp 2 5 2 Assignee; CubicCorporation, San Diego Primary ExaminerBenjamin A. Borchelt C lifAssistant ExamI'ner--S. C. Buczinski Att0rney-Carl R. Brown and Neil F.Martin [22] Filed: Mar. 8, 1971 21 Appl. No.: 121,794 ABSTRACT Distancemeasuring equipment that utilizes a light 152 US. Cl. ..3s6/5, 356/4,343 14, beam that is intensity d ted y a Carrier frequen- 343/5 DP250/217 SS cy which is frequency modulated by subcarrier [51] IHLCI lG01: 3/08 frequencies to provide accurate fine, medium, and [58] Fieldof 343/14 coarse distance measurements by detecting the phase 3436 6/217 shift of these carrier and subcarrier frequencies as a 313/108function of distance, and which system includes a cross coupling lighttransmission means for removing internal delay phase shift error, andthat employs a [56] References Clteq light attenuating device toequalize the intensity of the UNITED STATES PATENTS cross couplingillumination with the return illumination received, and that employs alight transmitter 3,547,539 Froome et al. having a substantially planarource 3,619,058 l1/l97l Hewlett et al. 3,l99,l04 8/1965 Miller ..343/5DP 20 Claims, 17 Drawing Figures TS T0 TRANSMITTER DIo DE 30 294 coARsE242 295 REFERENCE 21o INTERMEDIATE REFERENCE f f cRYsi'AL PHASE 2 BUFFER293 32 I OSCILLATOR DETECTOR vco FINE 236 226 238 240 REFERENCE /222ADDER TRANSMITTER REFERENCE CSZSSOING 290 DRIVER M XER DETECTOR 244LOGIC CLOCK4- INTERMEDIATE CLOCK 29B 300 COARSE ctocK PATENTED APR 1 7I973 SHEET 1 OF 6 Fig. 4

INVENTORS THOMAS s. MADIGAN RICHARD F. STONE DAVID c. DUNN WILLIAM F.HOLZER ROBERT H. SWEE ATTORNEYS PATENTEDAPR 1 1 19H 5. 728 025 SHEET 2[IF 6 Fig. 6

Fig. 8

INVENTORS THOMAS S. MADIGAN RICHARD F. STONE DAVID C. DUNN WILLIAM F.HOLZER ROBERT H. SWEET ATTORNEYS Fig. 7

PATENTEDAPR171975 3.7281325 SHEET 3 OF 6 lllllllllll mum lNVENTORSTHOMAS S. MADIGAN RICHARD F. STONE DAVID c. DUNN WILLIAM F. HOLZER 26ROBERT H. SWEET Fig. l3 BY ATTORNEYS BACKGROUND OF THE INVENTION Opticaldistance measuring equipment have been known and used for years. Theseequipments usually transmit light to the reflecting surface of a distantobject, receive the reflected light and then determine the distance tothe distant object from the phase shift of signals modulated on thelight signal transmitted and received. These equipments have varyingaccuracies that depend upon many factors, such as the accuracy of theentire system, phase shift delays in the equipment, the consistency ofthe frequency and amplitude output of the transmitting and receivingdevices, and many other factors. Yet these devices have manyapplications and have achieved wide spread use. Thus it is advantageousto have a new and improved optical distance measuring equipment that iscapable of providing more accurate distance readings in a relative- 'lyquick, efficient and inexpensive manner.

SUMMARY OF THE INVENTION In an embodiment of the optical distancemeasuring equipment of this invention, a light beam that may for examplebe in the infrared band, is transmitted to a reflector at a distantlocation, which reflector reflects the light back to a receiver. Thelight source of the light beam isintensity modulated by a carrierfrequency signal that is in turn modulated by subcarrier signals,preferably two signals. The phase in these three signals are detected bycross coupling the signals from the transmitter to the receiver. Thesesignals are so spaced in frequency range that a digital processingcircuit provides course, intermediate and fine distance measurements forimproved distance measuring accuracies. The plurality of distancemeasurements are averaged over a given number of samples, are totalizedand compared by digital means and then are decoded from binary to binarycode decimal output to provide a distance display in decimal numbers.The digital sampling and totalizing means provides relative rangebrackets that are within the capability of such a system. A singleoscillator, provides the frequency for the entire system reducingoscillator drift error.

There is usually an internal delay phase shift between the transmitterand the receiver that reduces the overall accuracy of the phase shiftdistance measurement. This invention provides means for removing thisinternal delay phase shift through utilization of a direct cross coupledlight transmitting means. Since this cross coupled light transmittingmeans is capable of directing a given intensity of light from thetransmitter to the receiver, that exceeds the intensity of the reflectedlight from a distant reflective object, means are provided forattenuating the light transmitted through the cross coupling device.

In many optical distance measuring equipments, as in the embodiment ofthis invention, a light emitting diode is employed as the lightgenerating means. This generated light is projected through a suitablelens to a distant reflector and returned to the receiver. The receiverthus views a particular minute portion of the light received that istransmitted from a minute area of the light emitting diode. Since givenminute areas of a p'hotodiode may generate light of varying intensitiesand phase, this can provide an error in the phase shift of themodulating signals that are transmitted and received. Thus in thisinvention means are provided that transform the light emitting diodelight source into a substantially planar light source.

It is therefore an object of this invention to provide new and improvedoptical distance measuring equipment.

It is another object of this invention to provide new and improvedoptical distance measuring equipment that provides a more accuratemeasurement of the distance to a reflective object.

It is another object of this invention to provide new and improvedoptical distance measuring equipment that averages a plurality of phaseshift measurement samples to provide a more accurate distancemeasurement.

It is another object of this invention to provide new and improvedoptical distance measuring equipment wherein a plurality of signals areimposed upon the transmitted light signal, which signals have differentfrequencies to provide coarse, medium and fine distance determinations.

It is another object of this invention to provide new and improvedoptical distance measuring equipment that has means for removinginternal delay phase shift from the distance measurement reading.

It is another object of this invention to provide new and improvedoptical distance measuring equipment having a cross coupled lighttransmission path for use in determining internal delay phase shifterror, which light transmission path adjusts the intensity of the crosscoupled light to even the intensity of the cross coupled light with theintensity of the light received from a distance reflective object.

It is another object of this invention to provide new and improvedoptical distance measuring equipment that provides transmitting lightwith a substantially planar light source.

It is another object of this invention to provide new and improvedoptical distance measuring equipment that utilizes a reflecting devicecapable of positioning reflectors at various angles to vertical whilemaintaining an exact centered light reflecting point over a givendistance measuring location.

Other objects and many other advantages of this invention will becomemore apparent upon a reading of the following detailed description andan examination of the drawings, wherein like reference numeralsdesignate like parts throughout and in which:

FIG. 1 is a diagram showing the measuring unit and reflector in use.

FIG. 2 is a top plan view of the measuring unit, partly cut away. V

F IG. 3 is an enlarged sectional view taken on line 3- 3 of FIG. 2.

FIG. 4 is an enlarged view of a light emitting diode, partly cut away.

F IG. 5 is an enlarged sectional view taken on line 5- 5 of FIG. 1.

FIG. 6 is a substantially diagrammatic side view of the measuring unit,showing the optical arrangement.

FIG. 7 is a diagram of an alternative means for integrating the lightfrom the transmitting diode.

FIG. 8 is a diagram of 'a further light integrating means.

FIG. 9 is anenlarged sectional view taken on line 9 9 of FIG. 3.

FIG. 10 is a front elevation view of a typical reflector unit.

FIG. 11 is a sectional view taken on line l1l1 of FIG. 10.

FIG. 12 is a sectional view taken on line l2-12 of FIG. 1 l.

FIG. 13 is a view of the rear control panel of the measuring unit.

FIG. 14 is a block diagram of the transmitter circuitry.

FIG. 15 is a block diagram of the receiver circuitry.

FIG. 16 is a block diagram of the digital readout circuitry.

FIG. 17 is a diagram showing phase shift determination.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus comprises ameasuring unit 10 and a reflector unit 12, which are set up at thelocations between which the distance is to be measured. As shown in FIG.1, a beam of light 14 is emitted from the transmitting lens 16 and thereflected beam 18 is returned to the receiving lens 20. The character ofthe light beam and the processing involved in determining distance aredescribed in conjunction with the circuitry.

The measuring unit is self-contained in a casing 22 having a front panel24 in which lenses l6 and are mounted, and a back panel 26 on which thecontrols are mounted. Any suitable portion of the casing may be maderemovable for access to the components. The lenses are conventional andare designed to focus the image of a light source at infinity, butadjustment may be provided for in any suitable manner. Adjacent the rearof casing 22 is a bracket 28 which supports an optical transmitter 30and an optical receiver 32 in axial alignment with lenses 16 and 20,respectively. The optical transmitter 30 is a light emitting diode, andreceiver 32 is a light sensitive diode, both types being available invarious forms and mountings. A typical arrangement is illustrated inFIG. 4, in which the transmitting diode is contained in a small can 34closed by a cover plate 36. The light emitting element 38 is in thecenter. Since the light from such an element will reach the focal planeof the associated lens with a slight phase deviation across theeffective disc of light, it is desirable to produce a light source withan effectively flat disc of small size to facilitate collimation. Thisis accomplished by mounting a small glass rod 40 in cover plate 36 inaxial optical alignment with the element 38, the light being conductedand integrated through the rod to the end face 42, which becomes theplanar light source.

For some uses the light can be integrated by means of a pin hole 44 in abaffle 46, as in FIG. 7, so that the light from the emitting element 48is essentially in a flat front at the plane of the baffle. Anotheralternative shown in FIG. 8, uses a field lens 50 to integrate the lightat an aperture 52.

Alignment of the measuring unit is made by means of a sighting telescope54 held in a socket 56 on top of bracket 28 and secured by a saddleclamp 58. The eyepiece end of telescope 54 fits into an eyepiece holder60 on back plate 26, and the objective end protrudes through front plate24 above and between the lenses.

Mounted on bracket 28 is a calibrating coupler 62, which couples thetransmitting and receiving diodes optically at selected times. Thecoupler includes an arm 64 mounted for rocking motion on a hollow shaft66, which is rotatable in the bracket on an axis between and parallel tothe optical axes of the diodes. Fixed in opposite ends of arm 64 areterminal sleeves 68 and 70 which hold the ends of an optical fiber link72, the link passing through a cylindrical head 74 on shaft 66. In thecalibrating position, the sleeve 68 holds the pick-up end 76 of link 72in front of transmitting diode 30, and sleeve 70 holds the emitting end78 of the link in front of receiving diode 32. The arm 64 is driven by amotor 80 fixed on bracket 28 and having a drive pinion 82 engaging agear 84, which is fixed to the arm. Motion of the arm 64 is limited bybumpers 86 and 88 on bracket 28, which hold the arm respectively in acalibrating position shown in broken line in FIG. 5, and a clearposition shown in full line. In the clear position, the diodes areunobstructed.

To attenuate the light intensity through the short link, the link 72 isinterrupted in the head 74 by a baffle 90, which slides axially in aslot 92. Baffle 90 has a slot 94 which is tapered, preferably with alongrithmic taper, to vary the exposed area of the opposed ends of theinterrupted link, as in FIG. 3. It should be noted that the size of theslot 94 is exaggerated for purposes of illustration, the actual widthvarying from essentially the full width of the link 72 to almost zero atthe narrow end. Due to the inherent losses in the fiber link and theaperture created by slot 94, the light through the link can be matchedto the light returning from the reflector. This avoids any changes inintensity between measuring and calibrating positions of the system. Thebaffle 90 is fixed in a cylindrical plug 96 which slides in hollow shaft66. An adjustment 98, rotatable in shaft 66, has a threaded end 100which is screwed into plug 96, the adjustment shaft being held againstaxial movement by a clip 102 riding in a groove 104. Fixed on shaft 98is a pulley 106, connected by a belt 108 to a pulley 110 on an actuatingshaft 112. The actuating shaft extends through a bearing 114 in backplate 26 and has a knob 1 16 for manual operation. This arrangementprovides a very fine adjustment for attenuation of the light, and thebelt drive allows for slippage at the limits of travel. The baffle 90has lugs 118 which project from head 74 and are engaged by spring 120which biases the baffle to the open position and prevents backlash inthe drive.

For convenience the various controls are on back panel 26, a typicalarrangement being shown in FIG. 13. In one upper corner is a distanceindicator 122, below which is a push button 124 for initiating ameasurement sequence. In the other upper corner is a dual purpose meter126, one function being to indicate battery condition when a batterytest button 128 is pushed. The other function is to calibrate the levelof reflected light to the reference light through the coupler 62.Another function is to aid in pointing the instrument for maximumreturned signal. By means of a selector switch 129, the level ofreflected light from the reflector unit can be read on meter 126 and theindicator adselector switch 129, the motor 80 is actuated to move thecoupler 62 to the calibrating position, so that the level of the lightthrough the coupling link is registered on the meter. Knob 116 is thenturned to actuate the attenuating baffle 90 and balance the light to thezero position. With the light levels thus calibrated, the unit is setfor making a distance measurement.

The reflector unit 12, shown in detail in FIGS. through 12, may be setup with any suitable number of reflector elements 132, three being shownas an example. Each reflector element 132 comprises a special prism 134secured in a holder 136, the holders being fixed in a group on amounting plate 138. The prism is a totally internal reflecting typeknown as a comer cube reflector, which reflects light precisely back tothe source, the configuration being well known. To facilitate mounting,the front portion 135 of the prism 134 is made cylindrical to fit intothe cup-like hold er 136. The inside face 140 of the front opening ofholder 136 is slightly divergent inwardly, so that the prism must beforced into place and snaps past the front edge of the holder to be heldsecurely. A recessed socket 142 in the rear of the holder cavityreceives the apex 144 of the prism and centers the prism in opticalalignment. Each holder 136 has feet 146 which are secured to mountingplate 138 by screws 148.

To provide for accurate alignment with the measuring unit, the reflectorassembly is adjustably mounted on a bracket 150, having a base 152, anupright post portion 154 and an upwardly extending arcuate arm 156. Themounting plate 138 is attached to a support block 158, which has anconvex arcuate channel 160 to slide on the inside of arm 156. Theassembly is held in place by a clamp block 162, having a concave arcuatechannel 164 to slide on the outside of arm 156, the clamp block beingclamped by a screw 166 which threads into support block 158 through aslot 168 extending longitudinally along the arm. Screw 166 has anenlarged head 170 for manual operation, and clamping pressure is appliedby a spring 172 between the head and clamp block 162. Base 152 has athreaded hole 174 to permit attachment of the bracket to a standardtripod, or for securement to a support member 176 by a retaining screw178, both indicated in broken line in FIG. 11.

For alignment purposes, the measuring unit is preferably mounted in ayoke 180, with a base portion 182 for attachment to a tripod, or to aprecision alignment device such as a surveyors transit mounting. Thisfacilitates careful aiming of the measuring unit at the reflector, usingthe sighting telescope. Equally precise alignment of the reflector unitwith the measuring unit is not critical, since the corner reflectorswill return offaxis beams to their source over. a reasonable angulardeviation.

The electronic circuit illustrated in FIGS. 14 and provides the signalsfor driving the respective transmitter and receiver diodes. Crystaloscillator 210 is a temperature compensated crystal oscillator thatsupplies an output signal with a frequencyfl, that for purposes ofillustrating a specific embodiment of this invention can be 4. 573198MHz. This output signalfl is fed to phase detector 220 that provides anerror signal output to drive the voltage controlled oscillator 212 at afrequency of 73. 17165 MHZ or frequency f2. Signal f2 is fed to buffer214 that raises the level of the signal to drive the subsequent logiccircuit. The 12 output of buffer 214 is fed to frequency divider 216that divides the frequency by' four, which signal is fed to thefrequency divider 218 that also divides the frequency by four, whichreduces the frequency f2 to that of frequencyfl or 4. 5731 98 MHz. Thephase detector 220 detects errors in phase between f2 divided by 16 andf1. Any phase difference between these signals provides an error voltageto the voltage controlled oscillator 212 that corrects its frequency andphase to phase lock frequency f2 and its phase to the frequency f1 andits phase of the crystal oscillator 210.

Crystal oscillator 210 also supplies signal frequency f1 through line222 to the series of frequency dividers 224, 228, 230, 232, 233 and 235.The first stage frequency divider 224 divides frequency fl by two to afrequency of for example in this description, 2. 286599 MHz and feedsthis signal to adder 226. Frequency dividers 224,228, 230, and 232divide frequencyfl to a frequency of 71. 456215.1(112 that is fedthrough line 234 to the adder 226. Thus the signal at 234 is f1 dividedby 64.

The output frequency f2 of VCO 212 provides the fine range signalfrequency that is 16 times fl and divider 224 provides an intermediaterange signal frequency that isfl over two and divider 232 provides acoarse range signal frequency of f1 over 64. The intermediate frequencyand coarse frequency are linearly added in adder 226 and are fed throughline 236 to frequency modulate the voltage controlled oscillator 212.This frequency modulates thef2 output signal that is fed through line238 to the transmitter driver circuit 240. Transmitter driver 240 is apower amplifier that supplies an output signal through line 242 to drivethe transmitter diode light source or transmitting diode 30, see P16. 2.The signal causes the light emitting diode to emit a light, which inthis embodiment is the infrared band, however it should be understoodthat any kind of light source that can be so energized and controlledmay be used. The signal through line 242, intensity modulates the lightsource by the f2 or 73. 171165 MHz carrier that is in turn frequencymodulated by the intermediate frequency and coarse frequency of theadder signal from line 236.

This transmitted light 14, see FIG. 1, is transmitted through thetransmitting lens in the manner previously described and is receivedthrough the receiving lens 20 and the receiving diode 32. The receivingdiode may be any suitable photo detector or other similar device capableof detecting the intensity modulation of the transmitted signal with thephase shift resulting from the distance moved to and from the reflectorunit 12.

The receiving diode 32 detects the intensity variation of the returnlight source modulated signal and provides an output signal that is fedthrough line 250, see FIG. 15, to [F amplifier 252, which intermediatefrequency amplifier has a band pass effect of amplifying and passing a73 MHz carrier that is frequency modulated by sub-carrier frequencies.The output of the IF amplifier 252 is fed to the data mixer 254.

The frequency dividers 224, 228, 230, 232, 233 and 235 divide the inputfrequency fl from line 222 to provide an output signal through line 247to the phase detector 258 of 8. 932 KHz that is the frequency f1 dividedby 512. The phase detector 258 provides an error signal to the voltagecontrolled oscillator 262, which voltage controlled oscillator providesan output signal of 73. 180097 MHz. The output of the VCO 262 is fedthrough the buffer 265 and through divider 260 that divides thefrequency down to the frequency of the input signal to the phasedetector 258, forming a second phase and frequency lock loop that holdsthe frequency and phase of the output signal of the VCO 262 to the samefrequency and phase of the output signal f1 from the crystal oscillator210. The phase lock of the phase detectors 220 and :58 hold the outputsof vco 212 and VCO 262 to the same phase, as set by the phase of thesignal fl from the crystal oscillator 210. Thus the output of VCO 262 toline 264 is offset from the output frequency f2 of VCO 212 by 8. 932KHz, but is frequency coherent.

The output signal from VCO 262 is fed through line 264 to phasemodulator 256. The same frequency signal is also fed through buffer 265to frequency divider 266, and the output of divider 266 that isessentially 2. 286878 MHz is fed to the phase modulator 256 to phasemodulate the carrier signal of 73. 180097 MHz received through line 264.Divider 268 also pro-. vides a signal to the phase modulator 256 of 71.4649 KHz that also phase modulates the carrier signal received from VCO262. The phase modulated output signal of phase modulator 256 issupplied through line 257 as a local oscillator input signal for thedata mixer 254.

The input signal from the receiver diode of line 250 is mixed in datamixer 254 with the local oscillator output of line 257 to provide anoutput carrier frequency of 8. 932 KHz that is amplitude modulated by afrequency of 279. 12 Hz and 8. 722 Hz. The output of the data mixer 254is amplified in the 8. 9 KHz band by IF amplifier 270 which output isfed through line 269 to detector 231 that provides amplitude detectionand the three components, namely the 8. 932 KHz carrier frequency thatis the fine data frequency, the 279. 12 Hz intermediate data frequencyand the 8. 722 Hz coarse data frequency is filtered by fine filter 251,intermediate filter 253 and coarse filter 255 to the respective zerocrossing detectors 276, 278 and 282. The zero crossing detectorsfunction to provide output signals for each zero crossing of the inputsignal or for each half cycle of the input signal, and supplies outputpulses to output lines 277, 279 and 281. The automatic gain controlamplifier 271 maintains the level substantially constant in the outputof the IF amplifier 270.

A portion of the output of the transmitter driver 240 is fed throughline 244 to reference mixer 246. Mixer 246 provides an output signal tothe zero crossing detector 291 of 8. 932 KHz. Thus the zero crossingdetector provides output pulses through line 290 of 8. 932 KHz for thefine reference signal. Frequency dividers 293 and 295 respectivelydivide the output of the zero crossing detector 291 to provideintermediate reference signal in line 292 of 279. 12 Hz and a coarsereference output signal in line 294 of 8. 722 Hz. A fine clock outputsignal supplied through line 296 has a frequency of 2,048 times the 8.932 KHz frequency. The intermediate clock signal output 298 supplies anoutput clock signal that is 2,048 times the intermediate referencefrequency of 279. 12 Hz and the coarse clock signal output in line 300provides an output signal that is 2,048 times the coarse referencefrequency of 8. 722 Hz.

It may be understood that output lines 290, 292 and 294 provide outputsignals with the original phase of the f1 signal from the crystaloscillator 210. The output lines 277, 279 and 281 have the phase of thereturn signals with the distance phase shift and also with any phaseshift resulting from internal delays in the circuits. The outputs oflines 296, 298 and 300 provide clock signals to clock the subsequentdigital readout and correlating circuit of FIG. 16, which clock signalshave a given multiple of the frequencies of the reference signals andthe data signals. For example this multiple for the fine clock signal is2,048 times the fine clock signal frequency of 8. 932 KHz.

Referring to FIG. 16, the signals with the original phase are fedthrough lines 290, 292 and 294 to the reference gate circuit-300. Thereturn signals with the distance phase shift and with theinternal delayphase shift is fed through lines 277, 279, and 281 to data gates 302. Aprogrammer 304 of known design that comprises known programming circuitsof NAND gates provides cyclic enable pulses for the coarse, intermediateand fine data gates and reference gates for each of the channels 290,292, 294, 277, 279 and 281. The programmer has three lines outputrepresented by the input lines 301 and 303 to the respective referencegates 300 and data gates 302. The programmer in known cyclic operationprovides enable levels through lines 301 and 303 to gate the inputsthrough lines 328 and 330 respectively to the data clock gate 306. Thedata clock gate 306 uses known techniques to provide a group of-NANDgates and NOR gates that select one of the clocks signals as establishedby the programmer signal through line 305, which clock signal throughone of respective lines 296, 298 or 300 is correlated with theparticular input reference signal and data signal gated throughreference gates 300 and data gates 302.

As a descriptive example, when the programmer 304, through lines 303 and301, select the gates of respective circuits 302 and 300 to gate thefine reference signals and the fine data signals through lines 328 and330 to the data clock gate 306, then the programmer also supplies theparticular gate signal through line 305 to gate the clock signals of thefine clock 296 to the data clock gate. The data clock gate 306,functions to open line 332 to an output signal, as follows. Withreference to FIG. 17, the fine reference signal 355, having a frequencyof 8. 932 KHz, opens the gate to line 332 with its leading edge 356. Theleading edge 358 of the fine data signal 357, closes the respective dataclock gate to line 332. The phaseshift 360 between the reference signal355 and the data signal 357, represents the phase shift of the distancemeasurement and the internal delay phase shift. During the period oftime that line 332 is open, fine clock pulses 362 of a very highfrequency which is 2,048 times the fine data and reference frequency of8. 932 KHz is gated to line 332. The fine clock signal is fed throughprogrammable divider 311 and provides pulses to the programmable up downcounter 310. With reference again to FIG. 17, it should be understoodthat pulses 362 of the fine clock are gated to line 332 during any updown portion of the respective reference and data signal 355 and 357such as at 364 and 366.

The programmer through line 334, programs the counter 310 to eithercount up or to count down. In this particular illustration, theprogrammer programs counter 310 to count up. The programmer 304 alsosupplies a program signal to divider 311 that divides down the countfrom the data clock gate by a given count, that for example may be 8,192counts.

For each gated count through line 332, and programmable divider 311, acount is supplied through line 309 to sample counter 308. After a givennumber of samples are counted, which number of samples counted by thesample counter 308 in this example is 8,192, then a signal is fed by thesample counter 308 through line 339 that advances the programmer to thenext clock data lines. Control signals from programmer 304 are fedthrough lines 336 and 337 to set the divider 311 and sample counter 308to the particular counts of the fine, intermediate and coarse data. Thussample counter 308 functions to count the sample groups out of dataclock gate 306 through line 309 and when the count is reached, then itadvances the programmer 304 to the next clock data line. Since theprogram divider 311 divides down in the same number as the samplecounter 308 counts, this provides an average of the input signal takenthat gives better data results and averages out input noise. The use ofthe trailing edges and leading edges of the reference signal and datasignals averages out harmonic noise. Thus the program counter 310, whichis a counter and temporary register, counts and registers the fine clockpulses for the given phase shift 360 and this phase shift is representedby the count in the counter 310.

Programmer 304 now sends a signal out through line 342 to the motor 80,see FIG. 5, that controls the position of the optical fiber length 72.This optical fiber length functions as a calibrating couplerrin themanner previously described. The output signal through line 342 causesthe motor 80 to rotate the calibrating coupler 62 to move the opticalfiber length 72 into calibrate position, that is to transmit the lightfrom the transmitting diode 30 to the receiving diode 32. The circuitdescribed in FIGS. 14 and 15 continue to operate in the same manner andprovide the same output signals as a distance measuring return signalwould provide. However the particular phase shift 360, as illustrated inFIG. 17, would if of smaller duration, be representative of that phaseshift caused by internal delay in the circuitry. The system takes itsreadings in the same manner as before, except the programmer 310 hassimultaneously supplied a signal through line 334 that programs the updown counter 304 to count down. Thus during this period of time, counter310 counts down with a number of counts during the programmed periodrepresentative of the internal phase shift delay, which count whenremoved from the count in the programmable up down counter 310 hasremoved this phase shift from the detected phase shift providing theactual phase shift delay count of the distance measurement. During thisperiod of time, no signals pass through latches 318 and 320 or to thebinary data register- 312. However a fine measurement has been taken anda calibration accomplished to remove the internal delay phase shift. Theprogrammer 304 then sends out a signal through line 342 that operatesthe motor returning the calibrating coupler and its optical fiber length72 to its original position where it is not in the optical path of thetransmitted light.

This same sequence of taking readings and counts from the intermediatedata and coarse data is accomplished in the same manner as previouslydescribed relative to the fine data to provide successive counts in theprogrammable up down counter with the calibration removed. It should beunderstood that the clock signals and thus the sample counts varybetween the fine, intermediate and coarse reference signals. Forexample, in the illustrative embodiment described, the particular countsfor the intermediate data is 256 and for the coarse data is 8.

The fine data count that has been stored in the programmable up downcounter 310, is supplied to, for example, latch 320 through line 319.Now assuming the intermediate measure has been made and as previouslydescribed, the clock counts for the intermediate data phase shift isstored in the programmable up down counter, then the 3 bit data, that isthe fifth, sixth and seventh most significant digits of the intermediatedata count, is switched through line 317 to the 3 bit latch 318. Theintermediate data count is always switched to the particular three bitlatch that was not used in first accepting the fine data count.

The outputs of latch circuits 318 and 320 are gated to decoders 322 and324 by a signal from the programmer 304 through line 385. These decodersof known technique and design have eight output lines for each decoder322 and 324. One output line on each of the output lines is selected andthese outputs are gated through gating network 326 of a known circuitemploying known techniques consisting of NAND gates that determinewhether to add zero, one or two counts to the intermediate data count incounter 310 to accurately correlate this particular significant digitreading with the data count of the previous fine count data inputregistered in the counter 310. Gating circuit 326 is gated by a gatingsignal from programmer 304 through line 385. This provides output pulsesrepresentative of zero, one or two counts that is supplied through line327 to counter 310. These pulses or counts correct the count in the updown counter 310 to correct for phase shift that may be beyond themid-point of the respective wave forms 355 and 357, which makes itdifficult to determine whether the phase shift is leading or lagging thereference signal.

After the pulses for the intermediate data are fed by line 327 toprogrammable counter 310, then the four most significant bits of thiscount are gated to register 312 by programmer 304 signal through line334. At the same time, the three most significant bits of theintermediate data signals and count in counter 310 are gated or loadedinto the latch circuit 320, which destroys the previous stored signal ofthe fine data and replaces it with the stored data of the intermediatedata count. Thus the intermediate data is stored in latch 320 to be usedlater. The intermediate calibration step is processed so that theinternal delay phase shift count of that signal stored in theprogrammable counter 310 is removed prior to the time that the signal isswitched into the binary data register 312.

The coarse measure is then made in the manner previously describedrelative to the intermediate measure and the fine measure, with thesignal count stored as described before in the programmable counter 310.The programmable counter in a known manner now gates the fifth, sixthand seventh most significant digits into the 3 bit latch circuit 318through line 317. The intermediate data count in latch 320 and thecoarse data count in latch 318 are again decoded by the programmer 304in the manner previously described and decoders 322 and 324 and gatingcircuit 326 again determines whether to add zero, one or two pulses orcounts into counter 310 through line 327. It is to be understood thatthe programmable up down counter 310 is, in the original condition downone count so that zero, one or two counts moves the counter in a rangefrom a down count of one to an up count of one. When the coarse counthas been corrected and stored in the programmable counter 310, then thefour most significant digits are stored into the binary data registerand down counter 312. This places a binary representation of a measureddistance, corrected for internal delay phase shift errors, in register312. The programmer 304 now feeds a count and enable signal through line386 to register 312 and BCD data register 314. This initiates the binarydata register 312 to count down and the BCD data register 314 to countup in binary code decimal, which changes the distance measurement tobinary code decimal in register 314. The BCD informa tion is thendecoded by decoder 316 with the measurement being displayed in decimalnumbers.

An exemplary sequencing of the described steps are as follows.

Fine calibrate Fine measure Load Latches Stored data in data register312 Intermediate measure Intermediate calibrate Correct intermediatedata count Store intermediate data count Coarse calibrate Coarse measureCorrect coarse data count Store coarse data count Convert stored fine,intermediate and coarse data to BCD and display It should be understoodthat in the digital system employed herein, in the exemplary embodiment,a 32 to 1 ratio between coarse, intermediate and fine data is possibleand provides a range that would have to be larger to the degree of beingimpractical if a decimal system was used.

Having described our invention, we now claim.

1. In an optical distance measuring device,

a light source,

transmitter means for sending a continuous light beam from said sourcetoward a light reflecting object whose distance is to be measured,

first means for generating a carrier frequency,

second means for frequency modulating said carrier frequency by asub-carrier frequency,

means for simultaneously modulating the intensity of said continuouslight beam by said carrier frequency and said sub-carrier frequency,

previously receiver means for receiving anddetecting the intensity ofsaid light beam from said reflecting object and providing data outputsignals, means for cross coupling said carrier frequency and sub-carrierfrequency from said first and second means to said receiver means, meansfor determining the relative phase shifts of said carrier frequency andsaid sub-carrier frequency reflected in the changes in intensity of theoutgoing and incoming continuous light beam, and means for combining thedetermined phase shift of said carrier frequency and the phase shift ofsaid sub-carrier frequency to indicate the distance. 2. In an opticaldistance measuring device as claimed in claim 1 including,

third means for simultaneously frequency modulating said carrierfrequency by a second sub-carrier frequency, said determining meansincluding means for determining the relative phase shifts of said secondsubcarrier frequency of the outgoing and incoming light, said crosscoupling means cross couples said second sub-carrier frequency, and saidcombining means includes means for combining the phase shift of saidsecond sub-carrier frequency with the phase shifts of said carrierfrequency and said sub-carrier frequency to indicate the distance. i 3.In an optical distance measuring device as claimed in claim 2 in which,

said combining means includes a binary digital processing circuit forprocessing said phase shifts to indicate distance,

and said carrier frequency and said first and second sub-carrierfrequencies are so spaced in frequency range that said digitalprocessing circuit provides v fine, intermediate and'course distancemeasuring accuracies. 4. In an optical measuring device as claimed inclaim 3 in which,

said combining means includes means for decoding the output of saidbinary digital processing circuit to binary code decimal and providingthe distance display in decimal numbers. 5. In an optical distancemeasuring device as claimed in claim 2 in which,

said first and second and third means includes oscillator means forproviding an output frequency, second oscillator means being phase andfrequency locked to said output frequency for providing said carrierfrequency, means for dividing said output frequency into saidsub-carrier frequency and said second sub-carrier frequency, and addermeans for simultaneously linerally adding said sub-carrier frequency andsaid second subcarrier frequency prior to frequency modulating saidcarrier frequency. 6. In an optical distance measuring device as claimedin claim 5 in which,

said determining means includes third oscillator means simultaneouslyphase and frequency locked to said output frequency for providing asecond output frequency,

frequency divider means for dividing said second output frequency intotwo frequencies, modulator means for modulating said second outputfrequency with said two frequencies, and mixer means for mixing theoutput of said modulator means and the carrier frequency and sub-carrierfrequencies in said data output signals. 7. In an optical distancemeasuring device as claimed in claim 6 in which,

said carrier frequency is a given multiple of said subcarrier frequency,and said sub-carrier frequency is the same multiple of said secondsub-carrier frequency. 8. In an optical distance measuring device asclaimed in claim 3 in which,

said digital processing circuit includes a binary counter for storingpulses, and gate clock means for providing a group of pulses to saidbinary counter that correspond in number to the time interval of saidphase shifts. 9. In an optical distance measuring device as claimed inclaim 8 including,

means for opening said gate clock means to pass a given number of groupsof said pulses, and divider means for dividing said pulses of said groupby said given number. 10. In an optical distance measuring device asclaimed in claim 8 including,

programmer means for gating said gate clock means serially for saidphase shifts of said carrier frequency and said sub-carrier frequencyand said second sub-carrier frequency. I 11. In an optical distancemeasuring device as claimed in claim 2 in which,

said combining means includes clock gate means for providing groups ofpulses having a number of pulses corresponding to the time length ofsaid phase shifts, counter means for counting said pulses, delay portionmeans for determining that delay portion of said phase shifts resultingfrom internal circuit delays in said measuring device, said clock gatemeans translates said delay portion into delay portion pulses,

and means for down counting said counter means in response to said delayportion pulses. 12. In an optical distance measuring device as claimedin claim 11 in which,

said delay portion means includes light transmission means for directlycros's coupling said outgoing light beam to said receiver means. 13. Inan optical distance measuring device as claimed in-claim 12 in which,

said light transmission means comprises an optical fiber link. 14. In anoptical distance measuring device as claimed in claim 13 including,

means for periodically pivoting said optical fiber link into and out ofthe light transmission position. 15. In an optical distance measuringdevice as claimed in claim 14 including,

light attenuating means in said optical fiber link for selectivelyattenuating the light intensity of the light transmitted. 16. In anoptical distance measuring device as claimed in claim l5 including,

means for ad usting said rght attenuating means to set the intensity ofthe light transmitted to substantiallythe light intensity of thereflected light beam. 17. In an optical distance measuring device asclaimed in claim 21 in which,

said light source comprises a light emitting diode, and light convertingmeans for translating the light emitted from said diode as a planarlight source. 18 In an optical distance measuring device as claimed inclaim 17 in which,

said light converting means comprises a relatively short in length lightpipe. 19. In an optical distance measuring device as claimed in claim 17in which,

said light converting means comprises a baffle with a pin hole. 20. Inan optical distance measuring device as claimed in claim 17 in which,

said light converting means comprises a baffle with an aperture and afield lens that integrates the light at the aperture.

1. In an optical distance measuring device, a light source, transmittermeans for sending a continuous light beam from said source toward alight reflecting object whose distance is to be measured, first meansfor generating a carrier frequency, second means for frequencymodulating said carrier frequency by a sub-carrier frequency, means forsimultaneously modulating the intensity of said continuous light beam bysaid carrier frequency and said subcarrier frequency, receiver means forreceiving and detecting the intensity of said light beam from saidreflecting object and providing data output signals, means for crosscoupling said carrier frequency and sub-carrier frequency from saidfirst and second means to said receiver means, means for determining therelative phase shifts of said carrier frequency and said sub-carrierfrequency reflected in the changes in intensity of the outgoing andincoming continuous light beam, and means for combining the determinedphase shift of said carrier frequency and the phase shift of saidsub-carrier frequency to indicate the distance.
 2. In an opticaldistance measuring device as claimed in claim 1 including, third meansfor simultaneously frequency modulating said carrier frequency by asecond sub-carrier frequency, said determining means including means fordetermining the relative phase shifts of said second sub-carrierfrequency of the outgoing and incoming light, said cross coupling meanscross couples said second sub-carrier frequency, and said combiningmeans includes means for combining the phase shift of said secondsub-carrier frequency with the phase shifts of said carrier frequencyand said sub-carrier frequency to indicate the distance.
 3. In anoptical distance measuring device as claimed in claim 2 in which, saidcombining means includes a binary digital processing circuit forprocessing said phase shifts to indicate distance, and said carrierfrequency and said first and second sub-carrier frequencies are sospaced in frequency range that said digital prOcessing circuit providesfine, intermediate and course distance measuring accuracies.
 4. In anoptical measuring device as claimed in claim 3 in which, said combiningmeans includes means for decoding the output of said binary digitalprocessing circuit to binary code decimal and providing the distancedisplay in decimal numbers.
 5. In an optical distance measuring deviceas claimed in claim 2 in which, said first and second and third meansincludes oscillator means for providing an output frequency, secondoscillator means being phase and frequency locked to said outputfrequency for providing said carrier frequency, means for dividing saidoutput frequency into said sub-carrier frequency and said secondsub-carrier frequency, and adder means for simultaneously linerallyadding said sub-carrier frequency and said second sub-carrier frequencyprior to frequency modulating said carrier frequency.
 6. In an opticaldistance measuring device as claimed in claim 5 in which, saiddetermining means includes third oscillator means simultaneously phaseand frequency locked to said output frequency for providing a secondoutput frequency, frequency divider means for dividing said secondoutput frequency into two frequencies, modulator means for modulatingsaid second output frequency with said two frequencies, and mixer meansfor mixing the output of said modulator means and the carrier frequencyand sub-carrier frequencies in said data output signals.
 7. In anoptical distance measuring device as claimed in claim 6 in which, saidcarrier frequency is a given multiple of said sub-carrier frequency, andsaid sub-carrier frequency is the same multiple of said secondsub-carrier frequency.
 8. In an optical distance measuring device asclaimed in claim 3 in which, said digital processing circuit includes abinary counter for storing pulses, and gate clock means for providing agroup of pulses to said binary counter that correspond in number to thetime interval of said phase shifts.
 9. In an optical distance measuringdevice as claimed in claim 8 including, means for opening said gateclock means to pass a given number of groups of said pulses, and dividermeans for dividing said pulses of said group by said given number. 10.In an optical distance measuring device as claimed in claim 8 including,programmer means for gating said gate clock means serially for saidphase shifts of said carrier frequency and said sub-carrier frequencyand said second sub-carrier frequency.
 11. In an optical distancemeasuring device as claimed in claim 2 in which, said combining meansincludes clock gate means for providing groups of pulses having a numberof pulses corresponding to the time length of said phase shifts, countermeans for counting said pulses, delay portion means for determining thatdelay portion of said phase shifts resulting from internal circuitdelays in said measuring device, said clock gate means translates saiddelay portion into delay portion pulses, and means for down countingsaid counter means in response to said delay portion pulses.
 12. In anoptical distance measuring device as claimed in claim 11 in which, saiddelay portion means includes light transmission means for directly crosscoupling said outgoing light beam to said receiver means.
 13. In anoptical distance measuring device as claimed in claim 12 in which, saidlight transmission means comprises an optical fiber link.
 14. In anoptical distance measuring device as claimed in claim 13 including,means for periodically pivoting said optical fiber link into and out ofthe light transmission position.
 15. In an optical distance measuringdevice as claimed in claim 14 including, light attenuating means in saidoptical fiber link for selectively attenuating the light intensity ofthe light transmitted.
 16. In an optical distance measuring device asclaimed in cLaim 15 including, means for adjusting said lightattenuating means to set the intensity of the light transmitted tosubstantially the light intensity of the reflected light beam.
 17. In anoptical distance measuring device as claimed in claim 21 in which, saidlight source comprises a light emitting diode, and light convertingmeans for translating the light emitted from said diode as a planarlight source.
 18. In an optical distance measuring device as claimed inclaim 17 in which, said light converting means comprises a relativelyshort in length light pipe.
 19. In an optical distance measuring deviceas claimed in claim 17 in which, said light converting means comprises abaffle with a pin hole.
 20. In an optical distance measuring device asclaimed in claim 17 in which, said light converting means comprises abaffle with an aperture and a field lens that integrates the light atthe aperture.